Redox flow batteries based on insoluble redox-active materials. A review

The ever-increasing demand for energy has stimulated the development of economical non-fossil fuels. As representative of clean energy, solar and wind have been identified as the most promising energy sources due to their abundance, cost efficiency, and environmental friendliness. The intrinsic intermittent of the clean energy leads to the urgent requirements large-scale energy storage technique. Redox flow batteries (RFBs) are attractive technology due to their independent control over energy and power. Insoluble redox-active flow battery is a new type of electrochemical energy storage technology that disperses redox-active particles in the electrolyte. Compared with traditional flow batteries, insoluble flow batteries have advantages of large energy density and are very promising in the development of large-scale energy storage systems. At present, three types of insoluble flow batteries have been explored: slurry-based flow batteries, metal/slurry hybrid, and redox-mediator-assisted flow batteries. This Review summarizes the research progress of insoluble flow batteries, and analyzes the key challenges from the fundamental research and practical application perspectives.